Gary wrote:
From: "Gary Wescom" <wescom@leblink.com>
Subject: [TowerTalk] Why preload guy lines?
This question has been bugging me for a while. I've been trying to figure
out
why tower guys are preloaded. I haven't worked out why that is an advantage
over simply tightening them enough to take up the slack. I run the math on
wind loading and such and the preload always seems to increase the stress on
the tower. There must be something I am overlooking.
Gary N0GW
As I understand it, the preload is simply intended to take out slack and
accomodate possible
stretch. I've been told it's set around 10% of the tensile strength of the
guy material,
taking overall structure loading into account.
Guy system preload certainly puts stress on the tower, but it should be a
small number compared
to the overall load on the structure. One of the problems is getting out
the catenary
sag. Most of it can be done visually...but how do you handle the last few
percent,
which contributes to slack, but can't be seen? (quarter inch downward
deflection
over a 100' guy won't be seen, but it contributes to slack.)
I would not be surprised to find the 10% number arbitrary. Similarly, I
would expect
the preload figure to vary with guy wire diameter. We tend to be operating
in a
fairly limited environment...towers 100' and under. So we tend to see 1/4
and 3/16 EHS
guys...and have an arbitrary preload number as a result.
Anybody see another explanation?
n2ea
jimjarvis@ieee.org
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